Under certain operating conditions, aircraft are vulnerable to the accumulation of contaminants on external component surfaces or skins. Examples of such contaminants include ice, water, and mixtures thereof. If left unchecked, the accumulation of ice can eventually so laden the aircraft with additional weight and so alter airfoil configuration as to cause undesirable flying conditions. The ability to detect the accumulation of ice on such surfaces, and the ability to measure the accumulated thickness thereof so as to identify dangerous flight conditions, has therefore become highly desirable.
A number of different kinds of contaminant detectors have been utilized for such objectives. Among them are capacitive ice detectors, examples of which can be found in U.S. Pat. Nos. 4,766,369 to Weinstein and 5,398,547 to Gerardi et al., both of which are hereby incorporated herein by reference.
The Weinstein invention is comprised of metal electrodes mounted near the outer surface of an aircraft. A small section of the outer surface is removed and replaced by embedding material which is preferably either plastic or an epoxy type material. The ice detector is embedded in the embedding material slightly below the outer surface. The electrodes do not touch each other and hence the presence of a material such as ice in the vicinity of the electrodes causes a change in the capacitance between the electrodes.
The Gerardi et al. patent discloses an ice sensor integrated in a pneumatic deicing boot. A short range sensor has positive electrode wires and ground wires separated by an electrical insulator, preferably neoprene. A long range sensor is fabricated from a series of positive electrode wires formed above guard electrode wires which are disposed above ground electrode wires. Two insulating sheets separate the three sets of wires. The wires and insulating sheets are configured and then potted in an elastic dielectric compound similar to RTV silicon. Gerardi et al. also states that conductive elastic fabric can replace the wires.
Efforts to improve such ice detection systems have led to continuing developments to improve their cost, manufacturability, reliability, usefulness, and efficiency.